Not Applicable
Not Applicable
Not Applicable
1. Field of the Invention
The invention pertains to microwave radio receiving and transmitting antennas. More particularly this invention pertains to dual-polarized, wide-band feed horns.
2. Description of the Prior Art
Microwave horns attached to the end of microwave waveguides have long been used as radio antennas for receiving an sending electromagnetic energy. Microwave horns also have been used as part of more complex antenna systems to feed, i.e. to send and receive, electromagnetic energy to and from reflectors or to and from dielectric or metallic electromagnetic lenses. In most applications the operational bandwidth of such waveguides and horns is limited to the range of frequencies of the electromagnetic waves that can propagate in a single, fundamental mode within the waveguide, without also being able to propagate in higher, different modes. In the prior art the operational bandwidth of these waveguides and horns has been broadened by including internal ridges within the waveguides and horns, which ridges increase the separation between the lowest frequency at which the fundamental electromagnetic mode will propagate within the waveguide and the lowest frequency at which a higher mode also will propagate. Typically, a probe or conducting post located within the waveguide electromagnetically couples a coaxial transmission line to the electromagnetic wave propagating within the waveguide.
The prior art also includes waveguides and horns having a circular or square cross-section that support the dual propagation of two orthogonal, fundamental electromagnetic modes that can be used to send and receive two, differently polarized waves of electromagnetic energy. Two, short conducting posts, or probes, located within the square or circular waveguide electro-magnetically connect two coaxial transmission lines to the two electromagnetic modes propagating within the waveguides. In such dual mode waveguides, the two probes typically are mounted at right angles to each other so that each probe will only excite, i.e. be electromagnetically connected with, one of the two fundamental modes propagating within the waveguide. In the prior art, because of physical and electrical problems, the two probes were located at different positions along the length of the waveguide, which difference in positions caused differences in the phase relationship between the two propagating modes that are excited by the respective probes, which differences in phase change as a function of frequency and, as a consequence, degrade the operation over wide bandwidths of such dual mode devices.
A report authored by J. K. Shimizu published in the IRE Transaction on Antennas and Propagation, vol. AP-9, pp. 223-224, March, 1961 describes an octave-bandwidth feed horn for a paraboloid that utilizes a horn having four internal tapered ridges. An article titled Broadband Ridged Horn Design, by K. L. Walton and V. C. Sundberg, published in Microwave Journal, vol. 7, pp. 96-101, March 1964 also describes the design of such horns and the Antenna Engineering Handbook, by R. C. Johnson, published by McGraw-Hill, at p. 40-4 presents curves showing the relationship between the wavelength of a mode propagating within a rectangular waveguide having four interior ridges and the dimensions of the ridges.
The present invention substantially reduces the phase differences between the two modes propagating within a dual mode, ridged waveguide and horn by locating the two probes within the waveguide at substantially the same position along the lengthwise dimension of the waveguide. The invention avoids electrical and mechanical conflict between the two probes by displacing or bending the center portions of the two probes in opposite directions.